[leetcode] Invert binary tree.

class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        TreeNode* temp;
        if(root)
        {
            temp=root->left;
            root->left=root->right;
            root->right=temp;
            if(root->left) invertTree(root->left);
            if(root->right) invertTree(root->right);
        }
        return root;
    }
};